DESCRIPTION (provided by applicant. Chemokines are induced in the infarcted myocardium and may play a role in inflammatory leukocyte infiltration, fibrous tissue deposition, and cardiac repair. Monocyte Chemoattractant Protein (MCP)-1, a potent mononuclear cell chemoattractant is rapidly upregulated in infarcts and may contribute to infarct healing. The CXC chemokine Interferon-gamma inducible Protein (IP)-10, a weak mononuclear cell chemoattractant, but potent angiostatic agent with anti-fibrotic properties, is markedly induced in the infarcted heart and may have a role in regulating infarct angiogenesis and fibrosis. This proposal will examine the role of MCP-1 and IP-10 in healing myocardial infarcts. Specific aim 1 will elucidate the functional role of MCP-1 in infarct healing, using gene-targeted animals in a murine model of myocardial infarction. MCP-1 may affect hematopoietic cells (predominantly mononuclear cells) as well as resident myocardial cells (fibroblasts and endothelial cells). In order to examine the relative importance of MCP-1 signaling in resident and blood-derived cells of the infarct, animals deficient in CCR2, the MCP-1 receptor, will be used to create chimeric mice after adoptive transfer of WT or CCR2 -/- bone marrow cells. In order to dissect the mechanisms responsible for suppressed macrophage activation and cytokine expression in the infarct we will test two intriguing hypotheses: a) that MCP-1 selectively recruits a specific monocvte subset [identified as CCR2 hi/fraktalkine receptor (CX3CR1) lo] that is more responsive to activation by inflammatory mediators, and b) that MCP-1 may directly regulate macrophage activation, differentiation and gene expression. These questions will be addressed using in vivo experiments with CX3CR1GFP/+ mice (in which GFP expression determines two distinct monocyte subpopulations in the bloodstream) and in vitro studies with isolated murine monocytes and macrophages. Specific aim 2 will investigate the role of IP-10 in healing mvocardial infarcts. Preliminary experiments suggest that IP-10 may be less important as a leukocyte chemoattractant. but may have a crucial role in preventing premature fibroblast accumulation and angiogenesis before the infarcted area is debrided and a fibrin-based provisional matrix, necessary to support fibrous tissue deposition is formed. This hypothesis will be tested using IP-10 and CXCR3 deficient mice;in addition the relative importance of IP-10/CXCR3 interactions in resident and hematopoietic cells infiltrating the infarct will be examined using chimeric mice with adoptive transfer of WT and CXCR3 -/- bone marrow cells. Specific aim 3 will explore the mechanisms responsible for the opposing effects of MCP-1 and IP-10 on fibrous tissue deposition using isolated cardiac fibroblasts and infarct myofibroblasts. The effects of MCP-1 and IP-10 on proliferation, migration and activation of cardiac fibroblasts and infarct myofibroblasts will be studied. Infarct myofibroblasts will be isolated from mice with defective MCP-1 (CCR2 and MCP-1 KO) and IP-10 (CXCR3 and IP-10 KO) signaling: their phenotvpe, motilitv, proliferative activity and gene expression will be compared with WT infarct myofibroblasts. Using gene microarray analysis, we identified novel actions of IP-10 in repression of genes associated with fibroblast adhesion, proliferation and migration. Accordingly we will study the effects of IP-10 on focal adhesion assembly and disassembly, fibroblast migration and proliferation. Understanding the role of chemokines in infarct healing may identify novel therapeutic targets aiming at optimizing cardiac repair and decreasing adverse remodeling.